1. Field of the Invention
The present invention relates generally to a system and method for controlling the attitude of a substrate. More specifically, the invention relates to a system and method for controlling the attitude of a disk-shaped substrate, such as a semiconductor wafer, an LCD glass wafer, a photo-magnetic disk, a compact disk and a minidisk.
2. Related Background Art
In a typical production process for a semiconductor equipment, there is widely adopted a substrate treatment system for sequentially transporting disk-shaped substrates (which will be hereinafter referred to as "wafers"), such as semiconductor wafers, which are to be treated, to a cleaning bath, in which a treatment solution, such as a chemical and a rinsing solution (a cleaning solution), is stored, and a drying section to clean and dry the substrates.
In order to efficiently clean a plurality of wafers, e.g., 50 wafers, using such a substrate treatment system, there is preferably adopted a method for transporting a plurality of wafers, e.g., 50 wafers, while causing the wafers to have the same attitude, i.e., while vertically arranging the wafers at regular intervals, by means of a wafer delivery unit, which is provided in a wafer delivery section provided between a wafer introducing/discharging section and a treatment section, and for carrying the wafers in and out of each of treatment units.
Therefore, there is known a conventional wafer attitude control system shown in FIG. 13. This wafer attitude control system comprises: a driving shaft b, which extends in directions of arrangement of a plurality of wafers W and which has a diameter so as to be receivable in a notch (a positioning notch) a for contacting the lower portion of the outer peripheral portion of each of the plurality of wafers W due to the weight of the wafers W to rotate the wafers W; idle pulleys c, each of which is rotatably provided so as to correspond to each of the plurality of wafers W and each of which is associated with the driving shaft b for supporting the corresponding wafer W to rotate in accordance with the rotation of the corresponding wafer W; and stoppers d, each of which contacts the outer peripheral portion of each of the wafers W moved downward due to gravity when the position of the notch a corresponds to the position of the driving shaft b after each of the wafers W is rotated, and each of which is associated with the corresponding idle pulley c to support the corresponding wafer W so that the driving shaft b does not contact the inner surface of the notch a of the corresponding wafer W (see Japanese Patent Laid-Open No. 6-345208).
However, in such a conventional system, the wafers W are rotated by the driving shaft b for a predetermined period of time to allow the notches a to engage the driving shaft b to align the notches a. Therefore, even after the notch a of one of the wafers W is arranged at a predetermined position, when the notches a of other wafers W are not aligned with each other, the driving shaft b remains rotating with respect to the wafer W, the notch a of which has been arranged at the predetermined position, until the notches a of all of the wafers W are aligned with each other. Therefore, the driving shaft b contacts the outer peripheral portions or notches a of a number of wafers W until the notches a of all of the wafers Ware aligned with each other. Consequently, there is a problem in that dust is produced to be splashed to adhere to the wafers W. In addition, since the driving shaft b is thin, it is easily worn down, so that there is a problem that the wear of the driving shaft b does not only obstruct the rotation of the wafers W, but it also obstructs the attitude control of the wafers W.
Such problems are common to the positioning of disk-shaped substrates other than the wafers W, such as photo-magnetic disks or compact disks.